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- 저자 : Zebene Lakew Teffera (검색결과 2 건)
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Mengesha Tsega,Awoke Guadie,Zebene Lakew Teffera,Yigez Belayneh,Dongjie Niu 한국산림과학회 2018 Forest Science And Technology Vol.14 No.3
This study was conducted to fit and evaluate ten existing nonlinear height diameter functions for Cupressus lusitanica in Gergeda forest Ethiopia. A total of 260 trees were measured for their diameter at breast height (D) and height using destructive sampling methods. This data were randomly split in to two datasets for model development (50%) and for model validation (50%). Considering hetroscadasticity of variance, all functions were fitted using weighted nonlinear least square regression. To evaluate the performance of each model, five fit statistics-such as Coefficient of determination (R2), root mean square error (RMSE), bias (E), absolute mean deviation (AMD), and coefficient of variation (CV%) were used. Among all the models tested, the Weibull type function of the form H¼1.3þa (1-exp (-bDc))þE was observed to give the best fit based on the model’s goodness of fit and predictive ability. Therefore, this model with three parameters has been conformed to provide reliable estimate of total tree height for Cupressus lusitanica in Gergeda forest, Ethiopia.
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Endashaw Workie Yihunu,Haiyan Yu,Wen Junhe,Zhang Kai,Zebene Lakew Teffera,Brhane Weldegebrial,Ma Limin 대한환경공학회 2020 Environmental Engineering Research Vol.25 No.3
The presence of high fluoride concentration (> 1.5 mg/L) in water causes serious health problems such as fluorosis, infertility, brain damage, etc., which are endemic to many places in the world. This study has investigated the fluoride removal capacity of the novel activated biochar (BTS) and hydrochar (HTS) using Teff (Eragrostis tef) straw as a precursor. Activated biochar with mesoporous structures and large specific surface area of 627.7 ㎡/g were prepared via pyrolysis process. Low-cost carbonaceous hydrochar were also synthesized by an acid assisted hydrothermal carbonization process. Results obtained from both adsorbents show that the best local maximum fluoride removal was achieved at pH 2, contact time 120 min and agitation speed 200 rpm. The thermodynamic studies proved that the adsorption process was spontaneous and exothermic in nature. Both adsorbents equilibrium data fitted to Langmuir isotherm. However, Freundlich isotherm fitted best for BTS. The maximum fluoride loading capacity of BTS and HTS was found to be 212 and 88.7 mg/g, respectively. The variation could primarily be attributed to a relatively larger Surface area for BTS. Hence, to treat fluoride contaminated water, BTS can be promising as an effective adsorbent.
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